Q10 of 82 Page 126

If f(x) = ax2 + bx + c and f(0) = 2, f(1) = 1 and f(4) = 6, then let us calculate the values of a, b and c.

We have,


f(x) = ax2 + bx + c …(i)


f(0) = 2


f(1) = 1


f(4) = 6


Replace x by 0 in equation (i), we get


f(0) = a(0)2 + b(0) + c


2 = 0 + 0 + c [ f(0) = 2]


2 = c


c = 2 …(ii)


Now, replace x by 1 in equation (i), we get


f(1) = a(1)2 + b(1) + c


1 = a + b + 2 [ f(1) = 1 & c = 2]


a + b = 1 – 2


a + b = -1 …(iii)


Finally, replace x by 4 in equation (i), we get


f(4) = a(4)2 + b(4) + c


6 = 16a + 4b + 2 [ f(4) = 6 & c = 2]


16a + 4b = 6 – 2


16a + 4b = 4


4 (4a + b) = 4


4a + b = 1 …(iv)


Solving equations (iii) & (iv), we get



-3a = -2



Put a = 2/3 in equation (iii), we get






Thus, a = 2/3, b = -5/3 and c = 2.


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